Bromination of benzene-series hydrocarbons



tBROMINATION F BENzENE-smigs Ludo K, Freyel t@111,111John William -Hml'und Mid? l c s M" .OTS t0 NofDrawing. Application Molzchf, 1.35m

' SeriaiNo. 15,2982

continuously. Furthermore, great care was rehas an' atomic weight 'lessthan *809 finoiu''s quired-incarnying out 4the brominationbecause monoand dinuciea'rlyla enatdbenze oftthe :yiollenceofv reaction at the end of the in.- mono-alikyl-substituted"behensg 'shaman duction period. Additional serious difculty is substituted be'zens' in wio-thehal'e enoounteiged in the process :beoause the .amtuentiscmorine;brornie dfnuori'n'i usual'- `ghotssic metal lhoude `does not separate readily 1y prsferredjts isratiol'mattes; "tritt hic from 4fthe xeaotion .products Vlout instead forms alkyl substituent 'fhy' riots lsixL moth @Apers tentjemulsion. '(ttons.v

lThe'fpririoipals.olojoot ofthe present-invention 'As ishereinbefore stated, a solution is lformed isto provide o method for tho bromnatoof by dissolving at istoiospsfoehft'ofhydroh benzene-series hydrocarbons and halogenated bromide in the compourlldwto be brominated,

more than two nuclear vvalkyl, substituents and 11,19 01' 5m@ @if Hude@ halogen Substitution p og tjs thereof ,isb'roniinated'by ar'lfirlnproved hod. ,Whoo the. oonponsitolho brominotod Y holo -hydrooorbon ooohfhologop has" .on om sweigrht less than The .brom'iation 'is ooon lohedf by contacting'-bromino--with a solution `,that consists essentillly of (1) at legst vpor"joofv Oflhydldgen bromide, `,ond (2') lot loostnolspor,oooh"ofvsoluminumohlorido, olumf num bromide; ferrie ehloride oijfei'jijio Abroniide in (3) the compound to be brominated.' (The terms parts andV p'eivcent are used herein be accomplished either at superatmospheric pressures or under vacuum.

When bromination is accomplished according to the method of the invention at a temperature as high as about 25 C. reaction takes place almost instantaneously, so that a contact time of only a fraction of a second is operable. If a reaction temperature lower than 25 C. is employed it is desirable to allow from 5 to 10 seconds for bromination to occur. In carrying out bromination according to the invention, the ratio of bromine to compound to be brominated is ordinarily selected from Within the range usually employed for batchwise -brominations of the prior art (i. e., from 50 to 75 per cent of the bromine theoretically required to accomplish the desired extent of bromination is ordinarily used). The reaction is operable for accomplishing mono- .bromination, dibromination or tribromination,

and the extent to which bromination is carried depends principally upon the proportion 0f bromine employed. Since an insufliciency of bromine is usually employed, it is advantageous to recycle unreacted starting material when a monobromination is to be accomplished, starting material and monobrominated material when dibromination is to Ibe accomplished and monobrominated and dibrominated material when tribromination is to be accomplished.

.Bromination according to the method of the invention is carried out in the absence of light, and is nuclear bromination. It is not essential that extreme care be taken `to avoid all light, because the opacity of bromine prevents catalysis of side-chain bromination by weak light. The reaction is conveniently effected in an iron reactor, although a glass lined reactor can be employed, as is essential in the prior art method.

The following examples illustrate and disclose preferred embodiments, but are not to be construed as limiting the invention:

EXAMPLE 1 ""A hydrocarbon of the benzene series having not more than two nuclear substituents was lbrominated according to the following procedure: f. Toluene (a total of 405 grams) was saturated with anhydrous ferrie chloride and anhydrous hydrogen bromide. Reaction was then effected by'niixing a stream of the saturated toluene with a stream of liquid-phase bromine (a total of 914 grains was used) at room temperature in a horiont'al tubular reactor having a series of Weirs to prevent free flow of the liquids through the tube; thebromine' was added through a tube extending through about one-third the length of the reactfor', and having openings along its full length. The' toluene and the bromine were added over a period of 61 minutes and the reactor was maintained 'about half full of liquid so that `the total utilized reaction volume was approximately 110 Products removed from the reactor were collected in a round bottom flask equipped with a reflux condenser. When all the bromine and toluene had been added the reactor was drained into the ask, and the reaction products were heated to separate hydrogen bromidetherefrom. The remaining liquid in the round bottom flask was then washed twice with distilled water and once with about a per cent solution of sodium carbonate. Fractionation of the bromnation products yielded 29 grams of toluene, 369 grams of monobromotoluene, 346 grams of dbromotoluene'and 68 grams of tribromotoluene.

A procedure similar to that described in the preceding paragraph was carried out using 249 grams of toluene, 755 grams of promine, and a total reaction time of 60 minutes. Fractionation of the products remaining after washing yielded 8 grams of toluene, 153 grams of monobromotoluene, 250 grams of dibromotoluene and grams of tribromotoluene.

EXAIVIPLEZ A series of brominations was conducted to show the applicability of the method of the invention to the production of a product substantially monobrominated or substantially dibrominated, according to the needs for these products, and to show the applicability thereof to the bromination of nuclearly halogenated compounds. Toluene was brominated by a one-step bromination, by a two-step bromination, and by a three-step bromination; the reaction was carried out by a procedure similar to that Idescribed in the first paragraph of Example 1. When bromination was accomplished stepwise all the toluene was subjected to the action of a portion of the bromine, and then the reaction products were subjected to the action of the remainder of the bromine. The results of this series of brominations are presented in Iable 1, below, which shows the amount of bromine, the amount of toluene, the number of passes (or bromination reactions), and the amounts of products produced.

A procedure similar to that described in the first paragraph of Example 1 was employed to brominate benzene (48.9 parts), saturatedwith vHBr and ferrie chloride, by the action of .bromine (51.1 parts). Fractionation of the nal product yielded 21 parts of benzene, 45 parts of mono-- bromobenzene and 4 parts of dibromobenzene.

EXAMPLE 4 A procedure similar to that described in the first paragraph of Example 1 was employed to brominate p-xylene (199 grams), saturated with I-lIBr and ferric chloride, by the action of bromine (196 grams) reaction was completed in 19 minutes. The fractionation' of the final product yielded 88.3 grams of unreacted xylene, 117.9 grams of monobromoxylene, 61.9 grams of dibromoxylene and 10.7 grams of higher boiling materials and residue.

EXAMPLE 5 A procedure similar to that described in the first paragraph of Example l Was used to brominate 1methylbutylbenzene (147 grams), saturated With I-IBr and ferrie chloride, by the action of bromine (131 grams) reaction was completed in l2 minutes. The fractionationof the final product yielded 77.7 grams of unreacted 1- methybutylbenzene, 92.1 grams of bromo(1 methylbutyl) benzene and 26.2 grams of higher boiling materials and residue. Infrared-analysis of the brominated material indicated that it is about 75 per cent pbromo lmethylbutyl)benzene and that the rest is probably the ortho compound. Bromo(l-methylbutyDbenzenes are believed to be new compounds. The mono-brominated product had a density of 1.2125 at 25 C., and boiled at 103 C. at 5 mm. Hg.

We claim:

1. A method of brominating a compound of the class consisting of hydrocarbons of the benzene series having not more than two nuclear alkyl substituents and monoand dinuclear halogen substitution products thereof wherein `the halogen has an atomic weight less than 80 that comprises contacting bromine with a preformed solution consisting essentially of (1) at least 0.05 per cent of hydrogen bromide and (2) at least 0.01 per cent o1 an amphoteric metal halide of the group consisting of aluminum chloride, aluminum bromide, ferric chloride and ferrie bromide in (3) the compound to be brominated.

2. A method as claimed in claim. l in which the preformed solution contains from 0.01 to 0.2 per cent of the amphoteric metal halide.

3. A method as claimed in claim 2 in which the preformed solution is saturated with hydrogen bromide.

4. A method vas claimed in claim 3 in which the compound brominated is benzene.

5. A method as claimed in claim 3 in which the compound brominated is toluene.

6. A method as claimed in claim 3 in which the compound brominated is a Xylene.

7. In a method of brominating a compound of the class consisting of hydrocarbons of the benzene series having not more than two nuclear alkyl substituents and monoand di-nuclear halogen substitution products thereof wherein the halogen has an atomic weight less than 80, in the presence of an amphoteric metal halide of the group consisting of aluminum chloride, aluminum bromide, ferrie chloride and ferrie bromide, the improvement that consists of dissolving at least 0.05 per cent of hydrogen bromide and at least 0.01 per cent of the amphoteric metal halide in the compound to be brominated and accomplishing the bromination by adding liquid bromine to the resulting solution at a temperature between and 80 C.

8. In a method of brominating a compound of 6 the class consisting of hydrocarbons of the benzene series having not more than two nuclear alkyl substituents and monoand di-nuclear halogen substitution products thereof wherein the halogen has an atomic weight less than 80 by contacting the said reactant with bromine in the presence of at least 0.01 per cent of an amphoteric metal halide of the group consisting of aluminum chloride, aluminum bromide, ferrie chloride and ferrie bromide, a procedure for eliminating the induction period normally required to initiate bromination which comprises dissolving at least 0.05 per cent of hydrogen bromide in the reactant prior to contacting it with bromine.

9. A continuous method for brominating a reactant of the class consisting of hydrocarbons of the benzene series having not more than two nuclear alkyl substituents and monoand dinuclear halogen substitution products thereof wherein the halogen has an atomic weight less than 80 which consists in forming a mixture of (1) at least 0.05 per cent of hydrogen bromide and (2) at least 0.01 per cent of an amphoteric metal halide of the group consisting of aluminum chloride, aluminum bromide, ferrie chloride and ferrie bromide with (3) the reactant, passing the resulting mixture in stream form through a reaction zone wherein it is maintained at a temperature between 10 and 80 C. and therein introducing liquid bromine into the owing stream, and separating brominated reactant from the effluent from the zone.

10. A process according to claim 9 wherein the reaction temperature is maintained between 25 and C.

LUDO K. FREVEL. JOHN WILLIAM HEDELUND.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,257,903 Dreisbach Oct. 17, 1941 2,273,467 Dreisbach Feb. 17, 1942 FOREIGN PATENTS Number Country Date 108,424 Austria Dec. 27, 1927 

1. A METHOD OF BROMINATING A COMPOUND OF THE CLASS CONSISTING OF HYDROCARBONS FO THE BENZENE SERIES HAVING NOT MORE THAN TWO NUCLEAR ALKYL SUBSTITUENTS AND MONO- AND DI- NUCLEAR HALOGEN SUBSTITUTION PRODUCTS THEREOF WHEREIN THE HALOGEN HAS AN ATOMIC WEIGHT LESS THAN 80 THAT COMPRISES CONTACTING BROMINE WITH A PREFORMED SOLUTION CONSISTING ESSENTIALLY OF (1) AT LEAST 0.05 PER CENT OF HYDROGEN BROMIDE AND (2) AT LEAST 0.01 PER CENT OF AN AMPHOTERIC METAL HALIDE OF THE GROUP CONSISTING OF ALUMINUM CHLORIDE, ALUMINUM BROMIDE, FERRIC CHLORIDE AND FERRIC BROMIDE IN (3) THE COMPOUND TO BE BROMINATED. 